To manage your email storage resources, you can implement a different HSM policy for each message server.

Messages and attachments are moved from a primary volume to the current secondary volume based on the age of the message.

The messages are still accessible.

Single-Copy Message Storage

Single copy storage allows messages with multiple recipients to be stored only once in the file system.

On UNIX systems, the mailbox directory for each user contains a hard link to the actual file.

Index Store [/opt/zimbra/index]

Data (MySQL) Store [/opt/zimbra/db]

Backup [/opt/zimbra/backup]

Log files [/opt/zimbra/log].

HSM Impact With Backups

Zimbra mailbox servers cannot see, read, or write to another Zimbra server. The HSM store data is integrated into the mailbox servers normal backup process - they are NOT separate processes. If you find the HSM disks are having an impact on your backup times and you need to get the backup times shorter please look at the following:

User submitted bug below. I don't think this is going to be possible but activity on the bug might push the dev's & PM's to pursue other options. I believe the current answer to the issue is above, Auto-group backups.

Nope. I'm not sure what else to add here. Don't know if there's actually a way to move them back.

Now What? Place In Cron

You will have to manually put in the zimbra crontab file a line to run the zmhsm command.

Something like the following at the end of the crontab [ su - zimbra ; crontab -e ] :

# HSM
0 6 * * * /opt/zimbra/bin/zmhsm -t

This will run every morning at 0600. The question of each administrator is what is the right time to run this. I'm initial thought is to try and kick it off after your backups. One might want to have two entries for the zmhsm command, one after your daily incremental and another time frame for you full backup days.

Checking For The HSM Zimlet

In the Admin web console, you'll see the reference to the HSM zimlets in this path:

Scheduling HSM Sessions

HSM can be configured for secondary storage volumes for older messages. Messages and attachments are moved from a primary volume to the current secondary volume based on the age of the message. Users are not aware of any change and do not see any noticeable difference when opening an older message that has been moved.

To manage your email storage resources, you can implement a different HSM policy for each mailbox server. The message age threshold for HSM is set globally on the HSM tab or for individual servers from the Server Volume tab. The default is 30 days. The thresholds configured on individual servers override the threshold configured as the global setting.
Sessions to move messages to the secondary volume are scheduled in your cron table. From the administration console, when you select a server, you can manually start a session, monitor sessions, and abort sessions that are in progress from the Volumes tab.

When you abort a session and then restart the process, the HSM session looks for entries in the primary store that meet the HSM age criteria. Any entries that were moved in the previous run would be excluded, as they would no longer exist in the primary store.